The US military has flown its own COVID-19 vaccine supply into the Northern Territory to inoculate Marines based in Darwin.
About 2200 servicemen and women are in the Top End as part of the annual Marine Rotational Force.
They've started receiving their first doses of the Moderna vaccine, which are being administered by US Navy medical officers.
The vaccine is offered under the US's emergency use authorisation to armed forces members who choose to receive it.
Many were already vaccinated before arriving in Australia as part of the US's ongoing vaccine rollout, which has fully inoculated about 49 per cent of the US's 328 million-strong population.
"We have received and administered these vaccines in an effort to fight against COVID-19," a Marine spokesman told AAP.
"(This will) protect the community in which we live and work, as well as our forces here in the Top End."
The US military has supplied enough Moderna vaccine for first and second doses.
The Australian government in May secured 25 million doses of Moderna in a bid to diversify the nation's vaccine portfolio from Pfizer and AstraZeneca.
All Marines are subject to strict screening and quarantine requirements prior to departure and on arrival into Australia.
They must present a negative COVID-19 test 72 hours before departure for Australia.
This is followed by mandatory 14-day quarantine in secure facilities at RAAF Base Darwin and nearby Bladin Village.
A small number of Marines have tested positive for the virus while in the NT and been transferred to the Howard Springs quarantine facility.
The 2021 deployment is the 10th annual Marine Rotational Force to be based in Darwin.
They are part of the ongoing posture initiative to promote regional stability under the ANZUS Treaty.
Darwin's location just south of more than a dozen Asian countries and some of the world's busiest shipping lanes makes it an ideal location for the force to be based.